Pulmonary hypertension (PH) is a significant cause of morbidity and mortality affecting a broad range of patients. Neonatal pulmonary hypertension is the second leading cause for admission to neonatal intensive care units for respiratory support. In adults, PH causes significant morbidity and mortality in patients with chronic obstructive pulmonary disease. In all patients, PH is characterized by cellular proliferation and altered vasoreactivity in the pulmonary vascular bed. The objectives of this proposal are to evaluate the vasodilator efficacy and toxicity of NO produced by virally mediated inducible nitric oxide synthase (iNOS) gene transfection in the lung and to determine the effect of virally transfected iNOS on the pathogenesis of PH. The general hypothesis is that virally transfected iNOS will result in sufficient NO formation to modulate pulmonary vasoconstriction and attenuate pulmonary vascular changes associated with pulmonary hypertension, but insufficient NO formation to result in toxicity. Utilizing human iNOS gene and, as a control, the E. coli lac Z reporter gene coding for beta-galactosidase (beta-gal) adenovirus constructs our goals set forth in this proposal are: 1) to optimize iNOS gene delivery and expression in the rat lung, 2) to determine the role of transfected iNOS on the development of pulmonary hypertension, and 3) to compare intravascular and intratracheal delivery of the iNOS gene in terms of gene expression, vascular reactivity and toxicity. These goals are addressed in the following specific aims: Specific Aim number 1: Assess the effectiveness of adenovirus-mediated iNOS gene transfection in attenuating acute pulmonary vasoconstrictor responses. Specific Aim number 2: Assess iNOS gene transfection-mediated effects on the development of chronic hypoxia-induced pulmonary hypertension. Specific Aim number 3: Assess the efficacy and toxicity of intravascularly and intratracheally administered adenoviral iNOS constructs. The methods will involve using adenovirus constructs containing the gene for iNOS or beta-gal that will be administered intravascularly; the lungs will then be studied to determine vascular reactivity, NO production, and localization of transfected iNOS. Some rats will be transfected and exposed to chronic hypoxia. Finally, intravascular and intratracheal delivery will be compared in terms of gene localization and toxicity.